Introduce common logic for Content.Source iterating over all chunks

[scrat98]

Jetty version(s)
12.0.8

Enhancement Description

Currently there are number of implementations that are doing the same thing: iterate over all chunks in Content.Source and make some transformation. Below the table with all those implementations

ByteBuffer asByteBuffer(Source source)                                                                                          ContentSourceByteBuffer
void asByteBuffer(Source source, Promise<ByteBuffer> promise)                                                                   ContentSourceByteBuffer
CompletableFuture<ByteBuffer> asByteBufferAsync(Source source)                                                                  ChunkAccumulator
CompletableFuture<ByteBuffer> asByteBufferAsync(Source source, int maxSize)                                                     ChunkAccumulator

CompletableFuture<byte[]> asByteArrayAsync(Source source, int maxSize)                                                          ChunkAccumulator

CompletableFuture<RetainableByteBuffer> asRetainableByteBuffer(Source source, ByteBufferPool pool, boolean direct, int maxSize) ChunkAccumulator

String asString(Source source)                                                                                                  ContentSourceString
String asString(Source source, Charset charset)                                                                                 ContentSourceString
void asString(Source source, Charset charset, Promise<String> promise)                                                          ContentSourceString
CompletableFuture<String> asStringAsync(Source source, Charset charset)                                                         ContentSourceString

InputStream asInputStream(Source source)                                                                                        ContentSourceInputStream

Flow.Publisher<Chunk> asPublisher(Source source)                                                                                ContentSourcePublisher

void consumeAll(Source source)                                                                                                  ContentSourceConsumer
void consumeAll(Source source, Callback callback)                                                                               ContentSourceConsumer

That may lead to the inconsistent behavior and multiplies surface of mistakes (for example ChunkAccumulator has a bug while ContentSourceByteBuffer don't have such bug #11756)

What do you think if it good idea to implement Content.Source iterating via Flow.Publisher as a reference and all other implementations will use it and just process chunks differently? It should also cover that issue #11755